Hey wow - I'm not asking a question!
DH just got back to me with my problem of why I was getting:
Can't connect to local MySQL server through socket '/var/run/mysqld/mysqld.sock' (2) dreamhosts
It was my fault!
When creating the new database, I used a quickie freeware program to generate a twenty digit password using lower, uppercase characters and digits, as well as any of the following :-)(+!?[*]%~"_
The problem arose with the use of double quotes " - the OSCommerce config didn't mind since it escpaed it out - but the dreamhost mysql server didn't like it for obvious reasons - thankfully it's fixed now.
So if you're getting similar errors to myself, have a look at the password.